WO2013191053A1

WO2013191053A1 - Method for discharge gas denitration

Info

Publication number: WO2013191053A1
Application number: PCT/JP2013/066195
Authority: WO
Inventors: 琴衣松山; 加藤　泰良; 今田　尚美; 啓一郎甲斐
Original assignee: バブコック日立株式会社
Priority date: 2012-06-19
Filing date: 2013-06-12
Publication date: 2013-12-27
Also published as: JP5916527B2; JP2014000522A; EP2862621A4; EP2862621A1

Abstract

A method for discharge gas denitration which can inhibit the deterioration of a denitration catalyst to be used for treating a discharge gas resulting from biomass combustion and which lessens the frequency of catalyst replacement, the method comprising blowing ammonia or urea as a reducing agent into a discharge gas resulting from combustion of biomass alone or of a mixture of a biomass fuel and coal and bringing the discharge gas into contact with a denitration catalyst that comprises titanium oxide as a main component, thereby reducing and removing the nitrogen oxides contained in the discharge gas, wherein sulfuric acid or SO₃ gas is injected into the discharge gas which is flowing on the upstream side of the denitration catalyst.

Description

Denitration method of exhaust gas

The present invention relates to a denitration method for exhaust gas, and more particularly to a denitration method suitable for denitration treatment of combustion exhaust gas generated when biomass is burned.

Global warming due to increased CO2 concentration in the atmosphere is proceeding at a faster rate than expected, and reducing CO2 emissions is an urgent issue. Measures to reduce CO2 emissions include reduction of fossil fuel consumption through energy saving, measures for using fossil fuels such as recovery and separation of CO2 in combustion exhaust gas, use of natural energy such as solar cells and wind power generation, etc. It is being advanced. In recent years, power generation using biomass as fuel instead of fossil fuel has attracted attention as a method that does not lead to an increase in CO2, and has begun to be adopted in the form of biomass burning or mixed combustion of biomass and fossil fuel, especially in Europe. .

By the way, biomass flue gas has the advantage of having a lower sulfur content than fossil fuels, but the combustion ash of plant-derived materials such as wood chips and beets contains alkaline inorganic salts, It is known to deteriorate. In particular, calcium carbonate has deliquescent properties, and its catalytic activity is reduced by soaking into the catalyst.

For example, when potassium ion of potassium carbonate soaks into a denitration catalyst for catalytic catalytic reduction with titanium oxide as the main component, potassium ion is first adsorbed to the adsorption point of ammonia (reducing agent) present on titanium oxide. It is known to inhibit the adsorption of ammonia and reduce the catalytic activity.

On the other hand, in the patent document 1, the applicant has reported a technique for delaying the decrease in catalyst activity by preliminarily adsorbing phosphate ions to the ammonia adsorption point of this type of catalyst. According to this, most of the potassium ions entering the catalyst first react with the phosphate ions adsorbed on the catalyst, and this reaction creates a new ammonia adsorption point on the titanium oxide. The decrease can be suppressed and the decrease in catalyst activity can be delayed.

JP 2011-161364 A

Incidentally, in Patent Document 1, a method of kneading or heating and kneading the catalyst (titanium oxide) and phosphoric acid in the presence of water is used in order to adsorb phosphoric acid on the catalyst surface before use. However, this method makes it impossible to replenish phosphoric acid on the catalyst surface during the treatment of exhaust gas. In other words, in order to maintain the catalyst activity at a certain level, periodic catalyst replacement work is required, and therefore a technique for reducing the frequency of catalyst replacement is required.

An object of the present invention is to suppress the deterioration of a denitration catalyst used for the treatment of biomass combustion exhaust gas and to reduce the frequency of catalyst replacement.

Here, in order to facilitate understanding of the present invention, the principle of denitration catalyst deterioration due to biomass combustion exhaust gas will be specifically described.

Most of the potassium attached to the catalyst exists as carbonate. This carbonate (hereinafter described as potassium carbonate (K ₂ CO ₃ )) is deliquescent at high humidity such as when the exhaust gas treatment device is started and stopped and enters the catalyst. Since the potassium ion of potassium carbonate that has entered the catalyst is bonded to carbonate ion, which is a weak acid, for example, it adsorbs to the OH group that is the adsorption point of ammonia on titanium oxide of the catalyst mainly composed of titanium oxide. Easy (Formula 1).
1 / 2K ₂ CO ₃ + HO-Ti- (active point on TiO ₂ ) → KO-Ti- + 1 / 2H ₂ O + 1 / 2CO ₂ (Formula 1)

On the other hand, ammonia, which is a reducing agent for the denitration reaction, is also adsorbed to OH groups (ammonia adsorption points) on titanium oxide (Formula 2). Here, since the adsorption power of potassium ions and ammonia to OH groups on titanium oxide is stronger for potassium ions, adsorption of ammonia to OH groups is inhibited by adsorption of potassium ions to OH groups. End up.
NH ₃ + HO-Ti- (active point on TiO ₂ ) → NH ₄ -O-Ti- (Formula 2)

Therefore, the present invention is characterized by spraying sulfuric acid (H ₂ SO ₄ ) or SO ₃ obtained by oxidizing SO ₂ gas into the exhaust gas upstream of the denitration catalyst. A part of the sulfuric acid sprayed in the exhaust gas in this way is decomposed into SO ₃ as shown in Equation 3 in the temperature range where the denitration catalyst is installed. Then, as shown in Equation 4, 5, potassium carbonate adhered to the denitration catalyst is gradually changed to potassium sulfate reacts with the added sulfuric acid or SO _3. Here, since potassium sulfate does not have deliquescence, even if it adheres to the catalyst, it does not easily move into the catalyst due to moisture like potassium carbonate. Even if potassium sulfate enters the catalyst, the potassium ion of potassium sulfate is hardly adsorbed to the OH group on titanium oxide because it binds to sulfate ion, which is a strong acid. Thereby, since the reduction | decrease of OH group which is an adsorption point of ammonia can be suppressed, the fall of catalyst activity (catalyst deterioration) can be made loose.

Specifically, in order to solve the above-mentioned problems, the present invention provides a denitration catalyst mainly composed of titanium oxide by injecting ammonia or urea as a reducing agent into exhaust gas obtained by burning biomass exclusively or by co-firing biomass fuel and coal. In the exhaust gas denitration method in which nitrogen oxides contained in the exhaust gas are reduced and removed by contacting with the catalyst, sulfuric acid or SO ₃ gas is injected into the exhaust gas flowing upstream of the denitration catalyst.

According to this, even during exhaust gas treatment, sulfuric acid or SO ₃ gas can be continuously or intermittently supplied to the catalyst surface accompanying the exhaust gas, so that it adheres to the catalyst surface or enters from the catalyst surface. The potassium ion can be continuously changed to potassium sulfate. Therefore, the catalyst activity can be maintained high for a long period of time, and the frequency of catalyst replacement can be significantly reduced.

In this case, the spray amount of sulfuric acid or SO ₃ gas is preferably adjusted so that the SO ₃ concentration in the exhaust gas flowing upstream of the denitration catalyst is 10 ppm or more and 100 ppm or less. Thus, it is possible to balance the effect and economy of sulfuric acid or SO ₃ gas.

According to the present invention, it is possible to suppress deterioration of the denitration catalyst used for the treatment of biomass combustion exhaust gas, and to reduce the frequency of catalyst replacement.

1 is a diagram showing a schematic configuration of an exhaust gas treatment apparatus to which an exhaust gas denitration method according to the present invention is applied.

Hereinafter, an embodiment of an exhaust gas denitration method to which the present invention is applied will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of an exhaust gas treatment apparatus to which the exhaust gas denitration method of the present embodiment is applied. The exhaust gas treatment apparatus of the present embodiment has a configuration suitable for treating the combustion exhaust gas of a boiler that performs, for example, exclusive combustion of biomass or mixed combustion of biomass and coal.

The exhaust gas treatment apparatus 1 of the present embodiment is connected to a boiler 3, a flue 5 through which combustion exhaust gas flows, a denitration device 7 disposed in the flue 5, and a flue upstream of the denitration device 7 5 and a sulfuric acid spraying device 11 disposed in the flue 5 between the reducing agent spraying device 9 and the denitration device 7.

The denitration device 7 is used, for example, by forming the denitration catalyst component into a honeycomb shape, or by applying it so as to fill a mesh with a metal substrate or ceramic fiber network processed into a mesh shape, The catalyst structure which laminated | stacked what shape | molded the spacer part in the above can be comprised. However, the form of the catalyst is not limited to this. The denitration catalyst component is not particularly limited. For example, titanium oxide is the main component, and tungsten (W), molybdenum (Mo), vanadium (V), phosphorus (P), aluminum sulfate, and the like are added as catalyst components. Those are preferred.

The reducing agent spraying device 9 sprays a reducing agent such as ammonia or urea from an injection nozzle 13 inserted into the flue 5. In this embodiment, an example in which ammonia is used as a reducing agent will be described.

The sulfuric acid spraying device 11 is connected to the sulfuric acid storage tank 15, the injection nozzle 17 inserted into the flue 5, and the storage tank 15 via the pipe 19, and the sulfuric acid extracted from the storage tank 15 is supplied to the injection nozzle 17. A pump 21 is provided for delivery. The pump 21 is configured such that the discharge amount of sulfuric acid is controlled by control means (not shown). The injection nozzle 17 may have any configuration as long as it can spray sulfuric acid in the flue 5 in a spray form. The position where the sulfuric acid spraying device 11 sprays sulfuric acid into the flue 5 is not particularly limited as long as it is upstream of the denitration device 7, but is downstream of the insertion position of the injection nozzle 13 of the reducing agent spraying device 9. It is preferable. Thereby, the influence (acid corrosion etc.) by the sulfuric acid of the injection | pouring nozzle 13 can be relieved.

The amount of sulfuric acid injected into the flue 5 from the injection nozzle 17 of the sulfuric acid spray device 11 varies depending on the potassium content in the biomass burned in the boiler 3, but the combustion ash adhering to the catalyst has a long residence time, Since it reacts gradually with SO ₃ in the exhaust gas, the concentration of SO _{3 in the} exhaust gas flowing in the flue 5 upstream of the denitration device 7 may be low, for example, the amount of sulfuric acid sprayed to be 10 ppm or more and 100 ppm or less. It is good to adjust. This is because if the SO ₃ concentration of the exhaust gas introduced into the denitration device 7 is lower than 10 ppm, the effect of suppressing the decrease in catalytic activity due to SO ₃ is reduced, while if it is higher than 100 ppm, the SO ₃ is excessively supplied. This is because there is a possibility that the economy is lowered and the equipment is corroded.

In the present embodiment, an example in which sulfuric acid is injected (sprayed) from the injection nozzle 17 of the sulfuric acid spraying device 11 will be described. However, instead of sulfuric acid, for example, SO ₃ gas obtained by oxidizing SO ₂ gas or ammonium sulfate is used. SO ₃ gas obtained by decomposition can also be injected, and the method for purifying the SO ₃ gas is not particularly limited.

In such a configuration, the boiler 3 is burned by supplying only biomass or both biomass and coal as fuel. The combustion exhaust gas generated by the combustion of the boiler 3 is guided to the denitration device 7 through the flue 5 to remove nitrogen oxides and the like in the exhaust gas. In the flue 5, ammonia is sprayed from the injection nozzle 13 of the reducing agent spraying device 9 and sulfuric acid is sprayed from the injection nozzle 17 of the reducing agent spraying device 9.

The sulfuric acid sprayed in the flue 5 is accompanied by the exhaust gas and reaches the catalyst surface of the denitration device 7, while the potassium carbonate contained in the combustion ash of the boiler 3 is accompanied by the exhaust gas and reaches the catalyst surface. Here, since the potassium ion of potassium carbonate reacts with sulfuric acid to become potassium sulfate having no deliquescence, it is unlikely to move into the catalyst. Even if it moves, it becomes difficult for potassium ions to be adsorbed to the OH group of the catalyst, which is the adsorption point of ammonia. Accordingly, by continuously or intermittently injecting sulfuric acid into the flue 5, a predetermined amount of ammonia can be continuously adsorbed on the catalyst, so that a decrease in catalyst activity can be greatly reduced. Moreover, since the performance of the biomass fuel exhaust gas treatment device 1 can be maintained high for a long period of time, the frequency of catalyst replacement can be greatly reduced.

Next, the present invention will be described in detail using embodiments of the present invention.

[Catalyst example]
Water was added to 1200 g of titanium oxide (Ishihara Sangyo, specific surface area 100 m ² / g), 108.1 kg of molybdenum trioxide, 79.1 kg of ammonium metavanadate, 553 g of silica sol (manufactured by Nissan Chemical, OS sol, containing 20 wt% as SiO ₂ ). In addition, after kneading with a kneader for 60 minutes, 207.4 g of silica-alumina ceramic fiber (manufactured by Nichias) was gradually added for 30 minutes to obtain a catalyst paste having a moisture content of 27%.

The obtained paste was subjected to metal lath processing on a 0.2 mm thick SUS430 steel plate, placed on a 0.7 mm thick substrate, and applied through a pair of pressure rollers to fill the mesh of the metal lath substrate. This was dried and calcined at 450 ° C. for 2 hours to obtain an initial catalyst. The composition of this catalyst is Ti / Mo / V = 93.5 / 5 / 4.5 by atomic ratio.

[Example 1]
In order to check whether potassium is sulfated by spraying sulfuric acid into the combustion exhaust gas of biomass and the decrease in catalytic activity is reduced, the catalyst obtained in the catalyst example is cut into 100 mm squares, and potassium sulfate is cut into this. Was impregnated so that the added amount of K ₂ O was 0.5 wt% with respect to the catalyst component, and then dried at 150 ° C.
Subsequently, the obtained catalyst was cut into a width of 20 mm and a length of 100 mm, and then three of them were used to measure the denitration performance under the conditions shown in Table 1, and the toxicity resistance against the potassium deterioration of the catalyst was evaluated.

[Comparative Example 1]
A catalyst was obtained in the same manner as in Example 1 except that the potassium sulfate in Example 1 was changed to potassium carbonate. The results of Example 1 and Comparative Example 1 are summarized in Table 2.

From the results shown in Table 2, the catalyst impregnated with potassium sulfate of Example 1 has a smaller decrease in denitration performance than that of Comparative Example 1 impregnated with potassium carbonate. This shows that potassium sulfate has less influence on the denitration performance than potassium carbonate. Therefore, it is clear that the durability of the catalyst is greatly improved if the potassium carbonate is changed to potassium sulfate by the method of the present embodiment.

[Example 2]
In order to confirm the effect of sulfuric acid spray, the following tests were conducted. First, the catalyst obtained in the catalyst example was cut into a 100 mm square, impregnated with an aqueous solution of potassium carbonate in an amount of 0.5 wt% as K ₂ O, and dried at 150 ° C.
Thereafter, the catalyst was cut into a width of 20 mm × 100 mm, filled into a reaction tube in a flow system, and exposed to gas under the conditions shown in Table 3. Here, as a gas condition, an aqueous sulfuric acid solution was injected so that the SO ₃ concentration in the gas was 100 ppm. Thereafter, the denitration performance of the obtained catalyst was measured under the conditions shown in Table 1, and the influence of sulfuric acid spray on the performance was evaluated.

[Comparative Example 2]
The same treatment was performed except that the sulfuric acid aqueous solution was changed to water under the conditions shown in Table 3 of Example 2. The results of Example 2 and Comparative Example 2 are summarized in Table 4.

When comparing Example 2 and Comparative Example 2, the decrease in catalyst activity in Example 2 is extremely small. Thus, it can be seen that the method of the present invention is effective in recovering the activity of a catalyst deteriorated by a large amount of alkali carbonate.

[Example 3]
In order to compare deliquescence under wet conditions, the following tests were performed. After sprinkling grass ash containing 20 wt% potassium carbonate uniformly on the surface of a 100 mm square cut to 1 g / m ² , sandwich the catalyst inside the two medicine wrapping papers, Crimped to the catalyst. The catalyst was cut into a width of 20 mm × 100 mm, filled into a reaction tube in a flow system, and exposed to gas under the conditions shown in Table 3. Here, as a gas condition, an aqueous sulfuric acid solution was injected so that the SO ₃ concentration in the gas was 100 ppm. Thereafter, the obtained catalyst was allowed to stand in a sealed container at 30 ° C. and 100% relative humidity for 100 hours, and then dried at 120 ° C. for 2 hours.
Subsequently, after removing the ash adhering to the obtained catalyst, potassium moved into the catalyst was measured by fluorescent X-ray.

[Comparative Example 3]
The same treatment was performed except that the sulfuric acid aqueous solution of Example 3 was changed to water. The results of Example 3 and Comparative Example 3 are summarized in Table 5.

From Table 5, the catalyst of Example 3 exposed to wet conditions after adding sulfuric acid upstream of the denitration catalyst was compared with the catalyst of Comparative Example 2 exposed to wet conditions without adding sulfuric acid. The amount of potassium transferred into the catalyst is very small. Thus, if the denitration method of this Embodiment is used, the fall of catalyst activity (catalyst degradation) by the moisture absorption of potassium carbonate containing ash can be improved significantly.

DESCRIPTION OF SYMBOLS 1 Exhaust gas treatment apparatus 3 Boiler 5 Flue 7 Denitration apparatus 9 Reducing agent spray apparatus 11 Sulfuric

acid spray apparatus

13, 17 Injection nozzle

Claims

Nitrogen oxides contained in the exhaust gas are reduced and removed by injecting ammonia or urea as a reducing agent into the exhaust gas mixed with biomass exclusively or biomass fuel and coal, and contacting with a denitration catalyst mainly composed of titanium oxide. An exhaust gas denitration method, wherein sulfuric acid or SO 3 gas is injected into the exhaust gas flowing upstream of the denitration catalyst.
The amount of spray of the sulfuric acid or SO 3 gas is adjusted so that the SO 3 concentration in the exhaust gas flowing upstream of the denitration catalyst is 10 ppm or more and 100 ppm or less. Denitration method.